1. Field of the Invention
The present invention relates to bonding tools for fine wire bonders. More particularly, the present invention relates to a novel ultrasonic transducer or sensor which is coupled to a fine wire bonding tool for use in a fine wire bonding machine.
2. Description of the Prior Art
Automatic wire bonders are well known and are used to make fine wire interconnections between a pad (or electrode) on a semiconductor device to a lead on a lead frame (or carrier). The bonding tools used in such machines are generally referred to as capillaries, used for ball bonding, or wedges used for wedge bonding. Both types of tools are most commonly mounted in ultrasonic transducers which assist in a scrubbing action while making bonds to the pads or leads to effect consistent bonds faster than if no ultrasonic assist had been used.
The bonding heads used to hold the prior art type transducers are quite heavy because they usually include wire clamps and a motor for effecting vertical or Z-motion of the bonding tool. Typical prior art bonding heads for bonding machines are shown in U.S. Pat. Nos. 4,653,681 and 5,360,155 which are incorporated herein by reference. The latter referenced patent employs a miniature piezoelectric vibrator element mounted in a miniature bonding arm which holds a conventional capillary. This piezoelectric element alone weighs three grams and it is estimated that the mounting arm weighs in excess of 30 grams. The bonding head system is mounted on an X-Y table which includes a mechanical actuating system that may weight several kilograms.
These prior art referenced bonding heads impose a large mass on the X-Y positioning motors, which in turn limits fast positioning of the bonding tool. It would be desirable to eliminate components which represent mass that is imposed on the X, Y and Z drive motors so that positioning of the bonding tool may be made faster with greater accuracy and less tendency of overshoot.
It would be desirable to provide a low mass transducer for bonding tools which permits faster positioning as well as lowering the mass of the bonding head components in a bonding machine.